This invention relates to digital-to-analog converters, and more specifically to optical digital-to-analog converters wherein an input signal is presented digitally, as a number of discrete multistate signals weighted by various powers of a radix, and converted to an output optical signal having an intensity, or amplitude, analogously determined by the number represented by the weighted input signals.
A digital-to-analog optical recorder is described in U.S. Pat. No. 4,257,111 to Soohoo. This patent discloses an apparatus for modulating a light source, in response to an electronic digital input word, for producing a continuum of output optical levels in which weighting and summing of the data bits is accomplished electronically. Such an apparatus is complex, and thus expensive to produce.
Several optical structures of interest are disclosed in U.S. Pat. Nos. 4,073,010; 4,071,907; 4,110,004 and 4,150,360. These patents generally provide optical systems in which various spatial filters are used to affect transmitted light. In U.S. Pat. No. 4,073,010 an electron beam addressed light valve produces a deposited charge pattern on a target, and a lens is used to obtain the fourier transform of the target image. A similar arrangement is provided in U.S. Pat. No. 4,071,907, where image information is detected by a linear array and fed to a switching network. The latter provides the signals from the array to a control electrode of an electronically addressed light modulator (EALM). Coherent light illuminates the charge pattern on a target of the EALM, and fourier transformation is obtained at a specific plane.
In U.S. Pat. No. 4,110,004, a complex spatial filter is shown in FIG. 9, in which an object transparency is at an input plane P1 and is illuminated by a collimated beam of light provided by a laser and a beam expander. U.S. Pat. No. 4,150,360 provides a two dimensional angular fourier transform spectrum of a transparent image.
Additional background art may be found in U.S. Pat. No. 3,512,871 in which diffracting cells are used in a fourier optics system, and U.S. Pat. No. 4,225,938 which teaches away from the use of a two-dimensional light valve in an optical processing system.
None of the known art, however, either discloses or suggests the use of an optical system to weight and sum the values associated with various bits of a digital data word, and specifically the use of such a system in conjunction with multistate optical gates controlled by the states of the discrete states of the input digital data word, to provide an output optical signal having an intensity which is analogous to the value of the input data.